Amphetamine, marijuana and secobarbital effect human aggressive and conversational behavior. However, the effects of these drugs on human cooperative responding remains to be examined. This proposal describes a free-operant laboratory procedure for examining the effects of these drugs on human cooperative responding. In the proposed studies cooperative responding will be established and maintained by experimental contingencies that schedule two periods. During one period subjects working alone can earn points exchangeable for money by pressing a button. During the other period subjects can either work with the other person or work independently. Working with the other person, the cooperative responses, will be maintained by points exchangeable for money added simultaneously to the subject's and the fictitious other partner's counter. Both counters will be visible to the subject. Working independently, the non-cooperative option, will be maintained by points exchangeable for money being added only to the subject's counter. Because the social context may modulate the effects of these drugs on cooperative responding a second eries of experiments will be conducted. In these experiments in addition to the options of working alone or with the computer-simulated other person subjects also will have the option of subtracting points from the fictitious other person. The computer- simulated other person will have the same options. The interacting effects of social context and drug dose will be examined by varying the cooperativeness/aggressiveness of he computer-simulated other person. These experiments extend the study of drug effects on human cooperative behavior to amphetamine, marijuana and secobarbital. The second series of experiments valuate whether social context determines drug effects on cooperative, and other social, responses. Cooperative responding is a social behavior vital to the functioning of human social and work groups.